[bigfudge]

The real issue here is the selection bias in the caseloads of good vs poor physicians. In psychological treatment teams it's common for the caseload to be (implicitly or explicitly) allocated based on the perceived skill of team members. Note — this may not necessarily correlate with their actual skill, but it still screws up any estimates of provider performance unless you have very good prognostic indicators of outcome from before treatment (and you likely won't).